Manipulation of suspended particles in fluidic microsystems is generally known and has for example been described by G. Fuhr et al in “Naturwissenschaften”, vol. 81, 1994, p. 528 ff. The microsystems form in particular channel structures through which a suspension fluid flows with the particles to be manipulated. As a rule the cross-sectional area of these channel structures is rectangular, with the width of the channel walls, which in operating position form the top and bottom (bottom/cover surfaces), being greater than the lateral channel walls (lateral surfaces). In the channel structures, microelectrodes are affixed to the channel walls, with high-frequency electrical fields being applied to said microelectrodes. Under the influence of the high-frequency electrical fields, based on negative or positive dielectrophoresis, polarisation forces are generated in the suspended particles, said polarisation forces making possible repulsion from the electrodes and, acting in combination with flow forces in the suspension liquid, making possible manipulation of the particles in the channel. As a rule, the microelectrodes of conventional microsystems are applied as straight electrode bands to the wider channel walls.
To generate the high-frequency electrical fields effective for dielectrophoresis, in each instance two electrode bands act in combination, said electrode bands being located at opposite channel walls, both with the same shape and alignment. For example the straight electrode bands are aligned parallel to the alignment of the channel i.e. the direction of flow of the suspension liquid in the respective channel section or at a predetermined angle transversely to the alignment of the channel. For an effective and safe formation of polaris at ion forces at the particles, the length of the electrode bands exceeds the characteristic dimensions of the particles to be manipulated many times over (by a factor of approx. 20 to 50).
Conventional microsystems have disadvantages in relation to the effectiveness of generating polarisation forces; the stability and longevity of the microelectrodes; and a limited ability of generating force gradients within the channel structure. These disadvantages are in particular linked to the electrode bands which are formed along comparatively long lengths in the channel. The longer an electrode band, the longer a particle flowing past is in the sphere of influence of the electrode band. Consequently, the effectiveness of the respective microelectrode or the field barrier generated by said microelectrode, increases. However, long electrode bands are also more susceptible to malfunction. Faults in workmanship or mechanical loads can cause interruptions which lead to electrode failure. Furthermore, to achieve a force effect which remains constant along the length of the channel, and thus a reproducible force effect, microelectrodes have so far been limited to the above-mentioned straight electrode shape.
Due to the disadvantages mentioned, the application of said fluidic microsystems with dielectrophoretic particle manipulation has been limited to guiding the particles in the channel structure or to deflecting particles from a given flow.